This invention relates to hyperthermia treatment of tissue by irradiation with microwave energy and ultrasonic wave energy and, more particularly, to applicators adapted for direct contact application of both microwave and ultrasonic wave energy.
Hyperthermia has received a great deal of attention in recent years as a form of cancer therapy. In hyperthermia, the temperature of a tumor is typically raised to the range of 42.degree. C. to 45.degree. C. Such temperatures can kill both malignant and normal cells. Hyperthermia is made practical by selective heating of tumors either alone or in conjunction with chemotherapy or radiation therapy. Microwave energy and ultrasonic wave energy have each been used to provide hyperthermia treatment. In either case, the malignant tissue must be heated to the desired temperature without overheating the surrounding normal tissue. External, or surface, applicators are preferable from a convenience standpoint.
In microwave hyperthermia, microwave energy has been applied to malignant tumors by various forms of applicators which act as antennas. The microwave energy is converted to heat in the tissue. Individual rectangular and circular waveguide sections having radiating apertures have been utilized for microwave hyperthermia treatment. However, individual microwave applicators have not been effective in heating deepseated tumors. Frequencies above about 500 MHz are rapidly attenuated in tissue and do not produce substantial heating at depths beyond about 1 or 2 cm. Lower frequencies experience less attenuation in tissue but cannot be focused with practical sized applicators. Furthermore, measurement of the temperature rise caused by microwave treatment is difficult. When thermistors and thermocouples are used, measurement errors are caused by interactions between the connecting wires and the incident microwave fields. Nevertheless, microwave hyperthermia has proven more or less satisfactory in some cases (for example, when the tumor is located fairly close to or at the surface).
Ultrasonic wave energy is more effective than microwave energy in penetrating to deep-seated tumors and can be focused to a small volume with practical sized applicators. Also, since electromagnetic radiation is not used, temperature measurements can more easily be made. However, ultrasonic wave energy is reflected almost completely at an air/tissue interface and at a tissue/bone interface. Therefore, certain tumor locations are, to a great extent, inaccessible to ultrasonic hyperthermia treatment.
It has become evident to researchers that microwave hyperthermia treatment is more suitable in some situations and that ultrasonic hyperthermia treatment is more suitable in other situations. Furthermore, situations are encountered where simultaneous treatment with microwave energy and ultrasonic wave energy is required. It is desirable to provide hyperthermia applicators which can be utilized in all these situations.
It is a general object of the present invention to provide novel applicators for hyperthermia treatment of tissue.
It is another object of the present invention to provide applicators for hyperthermia treatment of tissue by irradiation with microwave energy and ultrasonic wave energy.
It is yet another object of the present invention to provide applicators for efficient hyperthermia treatment of tissue under a wide variety of circumstances.